Effects of mechanical activation of inorganic gels on their thermal behavior. 2. Comparison of structure and thermal behavior between zirconia and titania gels

Changes in the temperature of crystallization, T_crys, due to mechanical pretreatment were entirely opposite between titania and zirconia hydrogels. The T_crys of the titania decreased by 18 and 44 K on rotation- and vibration-milling, respectively, while those for the zirconia increased by 14 and 18 K or 16 and 45 K, depending on the starting aqueous solutions, i.e., ZrOCl₂ or ZrO(NO₃)₂, respectively. These phenomena were discussed in terms of the microscopic phase transformation processes in noncrystalline gels during mechanical treatment. The difference between two hydrogels was concluded to be attributed to the differences in the geometry of the construction units, TiO₆ and ZrO₈, and the bond nature of metal-oxygen and metal-OH between TiO₂ and ZrO₂.